1. Field of the Invention
The present invention relates to a semiconductor device and a manufacturing method thereof, particularly, to a thin type semiconductor device having a large semiconductor pellet sealed with a resin and a manufacturing method thereof.
2. Description of the Related Art
In recent years, as the size of electronic devices are being drastically reduced, semiconductor devices, which are major electronic parts of the electronic devices, are being required to have large capacity and thin structure.
To allow a semiconductor device to have the large capacity, the size of a semiconductor pellet for use with the semiconductor device is being increased. In other words, the storage capacity of conventional semiconductor pellets for use with IC cards was around 4 kbytes. Recently, semiconductor pellets with the storage capacity of 1 Mbytes or more are being used. In this situation, the plane area of the semiconductor pellets exceeds 40 mm.sup.2. Thus, the area of a semiconductor pellet against the size of an IC card increases.
On the other hand, as thinning means for semiconductor devices, a structure where a semiconductor pellet is mounted on a so-called frame plate and they are sealed with a resin is popular from a view point of manufacturing cost. The frame plate is a thin insulation plate such as a conventional lead frame of which a plurality of semiconductor pellets are mounted on one main surface and a flat connection terminal block electrically connected to the semiconductor pellets is disposed on the other main surface.
However, when semiconductor pellets whose plane area exceeds for example 40 mm.sup.2 are mounted on a frame or the like and the semiconductor pellets are sealed with a resin by the transfer mold method, if the sealing thickness is reduced, the flowing characteristic of the sealing resin is remarkably deteriorated. Thus, it was very difficult to reduce the thickness of the semiconductor devices to 1 mm or less.
In other words, to reduce the thickness of a semiconductor device, a frame plate, a semiconductor pellet, and a sealing resin are thinned.
FIG. 3 is a sectional view showing a thin type semiconductor device. Reference numeral 1 is a frame plate with a thickness of around 0.25 mm. Reference numeral 2 is an adhesive layer disposed on one main surface of the frame 1. The thickness of the adhesive layer 2 is around 0.02 mm. Reference numeral 3 is a semiconductor pellet secured on the surface of the frame plate 1 with the adhesive layer 2. The thickness and plane area of the semiconductor pellet 3 are around 0.25 mm and 40 mm.sup.2, respectively. Reference numeral 4 is a wiring pattern disposed on the main surface of the frame plate 1. The wiring pattern 4 includes a connection pad. Reference numeral 5 is a bonding wire that electrically connects an electrode of the semiconductor pellet 3 and a connection pad of the wiring pattern 4. Reference numeral 6 is a flat type external connection terminal block disposed on the other main surface of the frame plate 1. Reference numeral 7 is a transfer mold type sealing resin that entirely covers and seals the semiconductor pellet 3, the bonding wire 5, the connection pad of the wiring pattern 4, and so forth. The height of the bonding wire 5 measured from the surface of the semiconductor pellet 3 is 0.15 mm or less. The height (thickness) of the sealing resin layer 7 is larger than the height of the bonding wire 5 by 0.03 mm or less.
Thus, theoretically, a semiconductor device with a thickness of 0.7 mm is structured. The thickness of the peripheral portion (thick portion) of the sealing resin 7 is around 0.45 mm. On the other hand, due to the deviation of the flow of the resin in the resin sealing process, a cavity portion takes place at the center portion (thin portion) of the sealing resin layer 7.
FIGS. 4 and 5 are plan views showing flows of a sealing resin in the case that a semiconductor pellet 3 with a plane area of 40 mm.sup.2 or more is mounted on a frame plate and sealed with a resin by the transfer mold method.
In a die 8, a pressure-fitted sealing resin (for example, bisphenol type epoxy resin compound containing inorganic powder as a filler) is melted and fluidized. As denoted by solid line arrows shown in FIGS. 4 and 5, the compound flows in the peripheral portion of the semiconductor pellet 3 with a relatively large space. Thus, this region is filled and coated with the compound.
On the other hand, since the space between the upper surface of the semiconductor pellet 3 and the die 8 is narrow the sealing resin does not properly flow (as denoted by dotted line arrows) and can not densely fill the space with the sealing resin. In particular, as semiconductor pellets are becoming large, this tendency is becoming strong. Thus, it is difficult to densely fill the space between the semiconductor pellet and the die with a sealing resin.
Consequently, when a sealed semiconductor device is mounted by an automatic mounting machine or the like, the semiconductor device tends to be broken.